A variety of refrigerant compressors for use in vehicle air conditioning systems are currently available. A popular vehicle compressor design is the variable displacement axial type. In this type compressor, a number of cylinders are equally angularly spaced about and equally radially spaced from the axis of a central drive shaft. A piston is mounted for reciprocal sliding motion in each of the cylinders. A piston rod connects each piston to a swash plate or wobble plate received about and operatively connected to the drive shaft. During operation of the compressor, rotation of the drive shaft imparts a radial reciprocating motion to the wobble plate. This driving of the wobble plate in a nutating path about the drive shaft serves to impart a linear reciprocating motion to the pistons. By varying the angle of the wobble plate relative to the drive shaft, the stroke of the pistons and, therefore, the displacement or capacity of the compressor may be varied to effect the desired compressing action.
One of the most efficient and successful vehicle refrigerant compressors of the variable displacement axial type in use today is that disclosed in U.S. Pat. No. 4,480,964 to Skinner, issued Nov. 6, 1984. During operation of this compressor, rotary motion from the engine is imparted to the compressor drive shaft through an external pulley. The compressor drive shaft is operatively connected to a journal plate assembly that imparts the linear, reciprocating motion to the pistons. The journal plate assembly includes a rotating driving plate and a non-rotating wobble plate in sliding engagement. The wobble plate is prevented from rotating by its engagement with a stationary guide rod aligned parallel to the axis of the drive shaft.
More specifically, the wobble plate engages the guide rod through a guide assembly including a spherical guide bearing mounted upon the guide rod and a pair of guide shoes. The guide shoes slidingly engage the outer peripheral surface of the guide bearing while resting in a slot having opposed semi-cylindrical bearing surfaces provided within the wobble plate. During compressor operation, the guide bearing reciprocates along the guide rod, while the guide shoes rock back and forth over the guide bearing. Thus, the radial-reciprocating motion of the wobble plate is accomodated by the action of the guide rod, the guide bearing and the guide shoes, assuring that only the desired back and forth motion is imparted to the pistons.
While this prior art compressor has proved very effective, there is some need for improvement. More specifically, under certain operating conditions and especially at higher speeds and loads, one of the guide shoes may be subjected to a disproportionately higher load than the other shoe. Such uneven loading serves to force the guide shoes to move relative to one another. More specifically, edges of the loaded shoe, and to a lesser extent the relatively unloaded shoe, may in fact be brought into frictional engagement with the guide rod in a line of contact. This frictional engagement reduces the operating efficiency of the compressor. Further, under certain operating conditions the engagement results in an undesirable increase in guide shoe wear. A need exists therefore for an improved guide assembly for a variable angle wobble plate compressor exhibiting improved wear characteristics.